Electrolytic shaping apparatus with cds surfaced electrode



NOV' 4 1969 ToMoYosHl MlKosr-.MBA ETAL 3,476,674

ELECTROLYTIC SHAPING APPARATUS WITH CdS SURFACED ELECTRODE Filed Sept.7. 1966 United States Patent O U.S. Cl. 204--224 13 Claims ABSTRACT oFTHE DISCLOSURE t?,

An electrolytic shaping apparatus is provided withl a working electrodehaving a CdS semiconductive A.layer thereon in order to improve theworking precisidnfrom about plus or minus 0.1 mm. to plus or minus 0.01mm.

This invention relates to an electrolytic shaping apparatus which has animproved electrolytic working electrode that provides improved workingprecision.

An electrolytic shaping treatment is known to shape a workpiece to thesame shape as that of a Working'electrode by means of electrolyticreaction which is performed by initially placing the electrode and theworkpiece Ain an opposing relationship therebetween and thereafter byflowing an electric eroding current from the electrode to the workpiecethrough an electrolyte provided therebetween.

A result working precision of a workpiece obtained from the electrolyticshaping treatment depends onta dimension of size of a working electrode.In other words, when a workpiece is treated with an electrode having acertain dimension of size, a dimension of size of the .treated workpieceis somewhat larger than that of the electrode. It is, therefore,necessary to form an electrolytic electrode to a little bit reduceddimension of size which will satisfactorily provide a treated workpiecewith an extreme desired dimension of size.

However, the formation of an electrolytic electrode to such a reduceddimension of size requires a hard calculation when an electrode has avery complex shape. There is also another defect in that electrolyticeroding velocities on respective surface portions of a workpiece differfrom each other in accordance with the difference in gaps between therespective surface portions of the workpiece and the electrode, sincesuch gaps are not equal with each other at the beginning of theelectrolytic shaping treatment.

One of the objects of this invention is, therefore, to provide a new andimproved electrolytic working electrode which may be formed to a desiredshape with an extreme desired dimension of size.

Another object is to provide an improved electrolytic shaping apparatusapplied thereto an improved working electrode, which solves theheretofore disadvantages as mentioned above.

Still another object is to provide an electrolytic shaping apparatushaving an improved working precision.

These and other objects and merits of the present invention will becomeapparent from following detailed descriptions taken in `conjunction withthe accompanying drawings, in which:

FIGURE 1 is a vertical sectional view of an electrolytic workingelectrode embodying the present invention;

FIGURE 2 is a vertical sectional View of another electrolytic workingelectrode shown in part thereof in accordance with the presentinvention;

FIGURE 3 is an enlarged vertical sectional view of the end portion of amodification of the electrode shown in FIGURE 2; and

3,476,674 Patented Nov. 4, 1969 FIGURE 4 is a schematic showing of anelectrolytic shaping apparatus embodying the present invention.

Briefly stated, this invention is characterized in providing asemiconductive layer on a working face of an electrolytic workingelectrode, thereby controlling eroding current in accordance with avoltage appearing across the semiconductive layer which corresponds to agap between the semiconductive layer and the workpiece.

The principle of the present invention will be hereinafter described indetail.

A voltage-regulator diode is well known to have a speciiiccharacteristic so that when an electric voltage having more than acertain intensity is applied thereto, such as a Zener break downvoltage, its resistance is abruptly decreased, and the electric currentflowing through the diode is increased. Some semiconductors also havesimilar sudden changes in the resistances thereof when a certainvoltage, such as, a building-up voltage, is forwardly applied to thesemiconductors.

An electrolytic eroding current flowing from a working electrode to aworkpiece through an electrolyte provided between the electrode and theworkpiece, may be represented by the following equation:

wherein h is a gap between the electrode and the workpiece, a is aconductivity of the electrolyte, and E is a voltage appearing across theelectrolyte.

According to the present invention, an electrolytic working electrode isprovided with at least one layer of semiconductive materials on aworking face thereof, so that the voltage E described before is alsoshown in the following equation:

wherein Eo is a voltage applied between the electrode and the workpiece,and Es is a voltage appearing across the semiconductive layer.

It is apparent that the voltage Es is changed proportionally to a gapbetween the electrode and the workpiece which corresponds to a volume orthickness of a resistive electrolyte existing in the gap. Therefore, ifan applied voltage Eo is more than the Zener break down voltage orbuilding-up voltage of the semiconductive layer, an electrolytic erodingcurrent may flow from the electrode to the workpiece through onlylimited surface portions of the semiconductive layer which are providedwith a voltage E of more than the Zener break down voltage or thebuilding-up voltage appearing thereacross. Accordingly, the working gapcan be constant over whole the surface of the workpiece whereelectrolytic reaction is provided thereon.

Now the improved electrode according to the present invention will bedescribed in detail.

FIG. 1 illustrates an electrode in accordance with this invention, theelectrode being provided with a voltageregulator diode on a working facethereof which opposes a workpiece. In this FIG. 1, 1 is a workingelectrode substratum, 1' is an electrolyte passage provided in thecenter of the electrode substratum 1 for conveying an K electrolyte ontoa surface of a workpiece which is to be workpiece is connected to thepositive pole thereof. An electrolytic eroding current is conductedthrough the electrolyte existing between the workpiece and theelectrode, thus the workpiece is eroded by means of electrolyticreaction.

As mentioned above, in this case, the working gap can be maintainedconstant by the action of the voltageregulator diode 2, so that aneroded surface of the workpiece can be made smooth with a goodprecision.

The dielectric layer 4 serves to prevent further machining of side endsof the workpiece which have been machined and contributes to animprovement of precision in eroding the side walls of the workpiece.

As seen from the description as mentioned above, a semiconductor insteadof the dielectric insulating layer 4 can provide the same effect as thatof the dielectric material from the viewpoint of precision improvement.

The semiconductive layer of a voltage-regulator diode is a diode with aP-N junction which is manufactured by methods, such as forming method,bond method, alloy method, crystal growth method, diffusion method, gasphase epitaxial growth method, etc., and is characterized in a thicknessof about 1p, a Zener break down voltage of 5 v., a charged fieldstrength of about 1 106 v./cm. and a current density of 100 a./cm.2 at aworking gap of 30p.

The diode is desirably coated with a chemically stable film of W or Auto prevent corrosion by the electrolyte.

FIG. 2. shows another electrode embodying this invention, in which aAu-Sn layer 5, a W layer 6, an Au layer 7 and a CdS semiconductor layer8 each having a thickness of 1 3 are deposited successively on a workingface of an electrode substratum 1 of Cu, Cu alloy or steel byevaporation, and Au is deposited nally on the CdS layer 8 to prevent theCdS layer from any change and deterioration of characteristics thereofdue to the electrolyte.

Various kinds of metals are interposed between the electrode substratumand the semiconductor layer 8 to prevent the semiconductor layer fromseparating from the electrode substratum due to the difference in thethermal expansion coefficients of both the electrode and thesemiconductor, thereby the CdS layer 8 is tightly provided on theelectrode substratum 1. The intervening layers 5, 6 and 7 are alsoarranged so that no unnecessary inuences may provide on the active CdSlayer 8.

When manufacturing another embodiment of the electrode shown in FIG. 2,a Au layer 7 is deposited on a working face of the electrode as shown inFIG. 3, a dielectric insulator layer 9 with a width of about 5 to 10 mm.is applied to the outer surface of Au layer 7, and a CdS semiconductorlayer 8 and another Au layer 10 for protectively covering the CdS layerare deposited thereon one after another. Near the periphery of the piledCdS layer and the Au layer 10, the CdS layer may preferably overlap alittle bit on the dielectric insulating layer 9, and the protective Aulayer 10 is preferably formed larger than the CdS layer but not largerthan the dielectric insulator layer in diameters thereof to prevent theAu layer 7 and the protective Au layer 10 from short-circuitingtherebetween.v

The resulting electrode is characterized in a maximum current density of10 a./cm.2 and a working gap of 20n- 30p from the characteristics ofCdS.

FIG. 4 is side sectional view of an example according to this invention.As shown in FIGS. 1 and 2, the semiconductor layer is necessarilyapplied to the surface of electrode 11. The electrode 11 is fitted tothe electrode supporting spindle 12 and moved at a constant speed (1-2mm./min. for the electrode as shown in FIG. 1 and 0.2 mm./min. for theelectrode as shown in FIG. 2) through a rack-and-pinion interlockingdevice 13 by a motor 14 for moving the electrode. A shank hole 16 isprovided for feeding the electrolyte to the electrolyte passage 18 ofthe electrode 11 by means of the electrolyte circulation pump 17.

When the electrode 11 is connected to the negative pole of a directcurrent source and the workpiece 15 to the positive pole thereof toperform the die-sinking machining, the electric current is conductedonly at the portion of gap of larger distance, the former gap beingmaintained constant to perform the machining. Thus, according to thisinvention, the protrusion of machined portions, which has hithertocaused problems, is improved remarkably and the working precision isimproved without any leakage current and a corrosion of the machinebeing employed.

Use of the present invention is very effective in industry. As mentionedabove, this invention avoids the trouble of overcutting and enable anincreased working precision from about 10.1 mm. to $0.01 mm. Since thecurrent iiowing through the semiconductor is constant when the electrodeis short-eircuited to the workpiece, the damage of electrode orworkpiece in the prior art can be prevented.

When a diode element having the above-mentioned forward characteristicsis used in this invention, the electrolytic machining can be performedby an alternating current by the use of its rectification action.Further, devices having resistance characteristics of a non-linear typecan also be employed to yield the same result as the voltage-regulatordiode.

As the semiconductor to be used in this invention, not only CdS used inthe example above-mentioned but also a semiconductor or semiconductorlilm, of which resistance decreases as the voltage increases, may beapplied.

We claim:

1. An electrolytic shaping apparatus comprising an electrode having aCdS semiconductive layer on a working surface thereof.

2. The electrolytic shaping apparatus of claim 1, further including aprotective coating on the outer surfaces of said CdS semiconductivelayer.

3. The electrolytic shaping apparatus of claim 2, wherein saidprotective coating includes a layer of gold.

4. The electrolytic shaping apparatus of claim 1, wherein anintermediate conductive layer is interposed between said working surfaceand said CdS semiconductive layer.

5. The electrolytic shaping apparatus of claim 4, wherein the peripheralportions of said intermediate conductive layers are coated with a layerof dielectric material, wherein said CdS semiconductive layer overliesonly a portion of said dielectric material, and wherein a protectivecoating is provided on both said CdS semconductive layer and saiddielectric material.

6. The electrolytic shaping apparatus of claim 1, further including apassageway through said electrode for directing a tiuid electrolyte fromsaid working surface to a workpiece.

7. The electrolytic shaping apparatus of claim 2, further including apassageway through said electrode for directing a uid electrolyte fromsaid working surface to a workpiece.

8. The electrolytic shaping apparatus of claim 4, further including apassageway through said electrode for directing a fluid electrolyte fromsaid working surface to a workpiece.

9. The electrolytic shaping apparatus of claim 4, wherein saidintermediate conductive layer consists of a material selected from thegroup consisting of Au, W and Au-Sn alloys.

10. The electrolytic shaping apparatus of claim 8, wherein saidintermediate conductive layer consists of a material selected from thegroup consisting of Au, W, and Au-Sn alloys.

11. An apparatus for electrolytically shaping a workpiece comprising aworking electrode, an electrolyte in fluid contact with said electrodeand the workpiece and means for applying an electrical current betweensaid electrode and the workpiece, said electrode having a CdSsemiconductive layer on a working surface thereof.

12. The apparatus of claim 11, wherein an alternate 3,202,599 8/ 1965Schierholt 204-224 current may be provided between said electrode andthe 3,236,756 2/1966 Beer 204-290 XR workpiece. 3,278,41 1' 10/ 1966Williams 204-290 13. The apparatus of claim 11, wherein a direct cur-3,284,691 11/1966 Schulz et al 204--224 XR rent may be provided betweensaid electrode and the 5 I workpiece. JOHN H. MACK, Primary ExaminerReferences Cited D. R. VALENTINE, Assistant Examiner UNITED STATESPATENTS US. CL X'R. 1,970,804 8/1934 Kerk ZOLL-290 10 204.443, 290

3,058,895 10/1962 Williams 204-143

